Recently, piperazine pyrophosphate is attracting attention as a component developing an excellent effect in a flame retardant composition added to synthetic resins. A number of reports have been made on the preparation of piperazine pyrophosphate.
For example, Patent Document 1 discloses a process in which piperazine hydrochloride and sodium pyrophosphate are allowed to react in an aqueous solution to give piperazine pyrophosphate as a sparingly water soluble precipitate. Patent Document 2 discloses a process in which anhydrous piperazine and anhydrous sodium pyrophosphate are allowed to react in an aqueous solution, and the reaction system is treated with hydrochloric acid to give piperazine pyrophosphate as a sparingly water soluble precipitate. Patent Document 3 teaches a process in which sodium pyrophosphate is treated with hydrochloric acid, and the resulting pyrophosphoric acid is allowed to react with hydrazine in an aqueous solution to form piperazine pyrophosphate as a sparingly water soluble precipitate.
In the processes disclosed in these references, however, it is difficult in practice to completely remove by-produced sodium chloride or sodium piperazine pyrophosphate by washing with water. It is known that, when piperazine pyrophosphate from a system containing a residual alkaline substance is applied to semiconductor devices, electronic equipment, etc., the alkaline substance generally gives adverse influences. Moreover, production by these processes involves high cost because (1) the production yield is low, (2) the raw materials are expensive, (3) waste disposal is costly, or (4) use of hydrochloric acid necessitates use of a glass-lined reaction vessel.    Patent Document 1: JP-A-48-88791    Patent Document 2: U.S. Pat. No. 3,810,850    Patent Document 3: U.S. Pat. No. 4,599,375